Severe Tropical Cyclone Graham

3 - 9 December 1991

Summary

Tropical cyclone Graham was the first cyclone of the year to be named by Perth TCWC and the first of three cyclones to have an impact on Cocos Island.

Late in November, an active pulse in the MJO developed over equatorial waters in the southern Indian Ocean. Convergence into the area was further assisted by a low-level cross-equatorial surge from the northern hemisphere. By 0000 UTC 2 December, a low pressure system had developed near 5°S 95°E tracking south-southwest.

Intensification of the low was rapid and at 0000 UTC 3 December, tropical cyclone Graham was named whilst located about 750 km northwest of Cocos Island. Within 24 hours, satellite imagery was indicating the development of an eye. Shortly thereafter, Graham commenced a gradual recurvature towards the southeast under the influence of a deep-layer anticyclone to the east. Maximum intensity was reached at 1500 UTC 5 December with mean winds estimated to be 65 m/s.

Tropical cyclone Graham made its closest approach to Cocos Island at 2300 UTC 5 December whilst located 150 km to the north-northeast. Although gales were reported on the island for a short period, damaging winds did not occur. The lowest MSLP recorded was 1004 hPa, indicative of the compact nature of the circulation.

As the cyclone tracked away from Cocos Island, it encountered strengthening upper-level westerly winds ahead of an advancing trough and began to shear. By 0000 UTC 8 December, the low-level circu- lation centre was fully exposed on the northwest side of the deep convection. Graham weakened below cyclone intensity at 1800 UTC 9 December although it wasn't until 10 December that the system was completely stripped of its central convection.